Field of the Invention
The present invention relates to an ignition coil, and in particular, relates to an ignition coil that supplies a high voltage to an ignition plug of an internal combustion engine.
Description of the Related Art
A magnetic circuit of a closed magnetic path configuration used in an existing internal combustion engine ignition coil is configured of a center core disposed inside a first coil and second coil, and a side core of which one end face comes into contact with one end face of the center core and another end face comes into contact with another end face of the center core across a magnet.
Other than this, there is a configuration such that a plate-form magnet with an area greater than a sectional area of the core is attached obliquely with respect to a magnetic path to a side core positioned outside a first coil and second coil, and disposed in a position intersecting on a perpendicular line equidistant from a central portion of a first coil and second coil winding, as disclosed in, for example, JP-A-10-275732 (Patent Document 1). According to the configuration disclosed in Patent Document 1, a position of a void is a position farthest from the first coil and second coil, because of which there is an advantage in that a decrease in binding due to an effect of magnetic flux leaking from the void can be reduced.
Patent Document 1: JP-A-10-275732
However, the internal combustion engine ignition coil disclosed in Patent Document 1 is such that a void is formed at either end of the magnet, and in the same way as the magnet, the void is formed obliquely with respect to the magnetic path. Because of this, magnetic flux leaking from one core end face reaches another core end face on an opposite side via the void, but as the orientation of the void is oblique with respect to the magnetic path, magnetic path length increases, magnetic resistance increases, and a magnetic property deteriorates. When wishing to reduce the magnetic resistance of the void portion, it is sufficient to reduce the magnet thickness, but there is a problem in that strength decreases, assembly becomes difficult, and productivity decreases.
Also, the internal combustion engine ignition coil is such that there is no projection or the like for positioning on a periphery of a void corresponding to a magnet insertion portion, because of which there is also a problem in that positional deviation of the magnet occurs due to an effect of magnetic force caused by magnetic flux generated when assembling a magnetic circuit or when energizing the first coil, and productivity and performance decrease. In order to solve this problem, there is a method whereby the magnet and core are fixed with an adhesive, but equipment for applying the adhesive is necessary, and a cost of a production line increases.